Circuit breakers with improved trip mechanisms



A. J. PASTENE Dec. 13,1966

CIRCUIT BREAKERS WITH IMPROVED TRIP MECHANISMS 2 Sheets-Sheet 1 FiledDec. 21, 1964 Dec. 13, 1966 A. J. PASTENE CIRCUIT BREAKERS WITH IMPROVEDTRIP MECHANISMS 2 Sheets-Sheet 2 Filed Dec.

62c 48a 54 62a 50 United States Patent 3,292,118 CIRCUIT BREAKERS WITHIMPROVED TRIP MECHANISMS Alexander J. Pastene, Milwaukee, Wis., assignorto Cutlet-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware FiledDec. 21, 1964, Ser. No. 419,874 20 Claims. (Cl. 33537) This inventionrelates to circuit breakers land more particularly to improved tripmechanisms therefor.

Circuit breakers of the type contemplated by this invention are providedwith an operating handle manually movable between an on and off positionto close and open the contacts. An overcenter mechanism is activated bythe operating handle to effect the contact operation. A latch isprovided which when engaged with the overcenter mechanism actstherethrongh to maintain the contacts closed. These breakers are of thethermal and magnetic trip type whereby they respond to a continuoussmall overload current or respond magnetically to -a large overloadcurrent to effect disengagement of the latch. As a result, theovercenter mechanism is activated or tripped to cause opening of thecontacts to interrupt and thereby protect the associated circuit fromexcessive currents. Such tripping action also causes the operatinghandle to be moved from its on position to indicate the trippedcondition.

A characteristic feature of one type of circuit breaker with which theinvention can be used is that the latch is unstable, this instabilitybeing desirable and advantageous in that it affords significantly moreaccurate control of the tripping point of the breaker. To maintainengagement of the latch, it is necessary to apply a bias .force thereto.The apparatus which normally applies such bias force is controlled bythe thermal or magnetic overload current responsive mechanism to reduceor remove such force thereby to permit disengagement of the unstablelatch. Then the latch can be reengaged after the thermal member hascooled sutficiently. While means for applying the bias force to theunstable latch such as that dis-closed in Martin F. Koenig et al. PatentNo. 3,081,386, dated Mar-ch 12, 1963, has been found satisfactory, ithas been found desirable to improve the function of the bias forceapplying means and particularly its cooperation with the thermal andmagnetic overload current responsive mechanism to improve the accuracyand reliability of the tripping action. These improvements are realizedby providing an improved structure which is effective, in addition totransmitting. a bias force to the unstable latch, to permit trippingmagnetically without disturbance or requiring respouse from thethermally responsive member and to reduce the stress on the thermallyresponsive member as it heats and to relieve the thermally responsivemember of all external mechanical stress on tripping of the breaker toprevent formation of a set.

A characteristic feature of another type of circuit breaker with whichthe invention can be used is that the latch is stable, such as thebreaker shown in FIGS. 7. In this type of breaker, due to the stabilityof the latch, the tripping means must apply a force to pull the lat-chopen when an abnormal electrical condition occurs. While means forpulling a circuit breaker latch open have been known hereto-fore, it hasbeen found desirable to improve the function of the unlatching forceapplying means and its cooperation with the thermal and magneticoverload current responsive elements to improve the accuracy andreliable repeatability of the tripping action. These improvements arerealized by providing an improved structure in many ways similar to thestructure used in conjunction with the unstable lat-ch breaker andPatented Dec. 13, 1966 which is effective to cause tripping magneticallywithout disturbing or requiring response from the thermally responsivetripping member and to relieve the thermally responsive member of allexternal mechanical stress upon tripping of the breaker.

In employing a stressed spring member in the structure undesirable lostmotion is effectively eliminated to reduce susceptibility to trippingunder mechanical shock and enhanced precision and reliability ofresponse to overload currents is attained.

Accordingly, a general object of the invention is to provide novel meansfor affording the aforementioned improved results.

A more specific object of the invention is to provide means forincreasing the accuracy and reliability of response of a circuit breakerto excessive heating or currents, by removing external stress on thethermal member following tripping thereby to avoid subjecting thethermal member to a stress larger than it can safely withstand.

Another specific object of the invention is to provide novel means formaintaining engagement of the latch mechanism in a circuit breaker andfor cooperating in an improved manner with the current responsivemechanism to enhance the operating reliability of the breaker.

Another specific object of the invention is to provide in a circuitbreaker means for applying a force between the thermal member and thelatch to maintain engagement of the latter which force applying meansdoes not create stress in the thermal member after tripping and which isfreely movable with the thermal member upon flexure of the latter underexcessive current flow.

A characteristic of the invention is to provide a circuit breaker havingthe aforementioned advantages and in which lost motion in the trippingmechanism can be eliminated or minimized.

Other objects and advantages of the invention will hereinafter appear.

These and other objects and advantages of the invention and the mannerof obtaining them will best be understood by reference to the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings, wherein:

FIGURE 1 is a front elevational view of a circuit breaker of theunstable latch type with the cover removed to show the internalmechanism, constructed in accordance with the invention;

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1 showingthe two spring biased slide plates forming part of the trippingmechanism;

FIG. 3 is an isometric view of the two slide plates of FIGS. 1 and 2;

FIG. 4 is a top view of a modified slide plate usable in place of theupper slide plate in FIGS. 1 and 3;

FIG. 5 is a fragmentary front elevational view of a circuit breaker ofthe stable latch type with a portion of the cover removed to show amodified internal mechanism; j

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5 showingthe two spring biased slide plates forming part of the trippingmechanism of the modified breaker; and

FIG. 7 is an isometric view of the two slide plates of FIGS. 5 and 6.

Referring to FIG. 1, there is shown a single pole circuit breaker havingan insulating housing comprised of a shallow base 2 having an open sideclosable by an insulating cover 4, the latter being shown in FIG. 2 andbeing removed in FIG. 1 to show the internal mechanism of the breaker.The cover is rigidly secured to the base by a plurality of rivets 6 orthe like. Base 2 and cover 4 are 'ice provided at the top portionsthereof with cut-out portions in registration forming a rectangularelongated opening for accommodating an operating handle 8 which extendsto the exterior of the housing. Handle 8 is provided with a rectangularopening 10 therethrough for receiving a handle tie when a plurality ofsingle pole breakers are assembled in plural-pole relation. For anillustration and description of certain portions of the operatingmechanism including the contacts and overcenter mechanism which areshown but not described in detail herein, reference may be had to theaforementioned patent.

As shown in FIG. 1, the breaker is provided with a latch 12 pivotallysupported on and suspended from the lower right-hand portion ofoperating handle 8. An inverted U-shaped latch lever 14 is arranged forcooperation with latch 12 to maintain the contacts closed when theoperating handle is in its extreme counterclockwise position as shown inFIG. 1. Latch lever 14 is pivoted at the lower end of its left leg inthe base. A terminal bracket 16 is rigidly and electrically connected atthe upper end thereof to the upper end of a thermal responsive membersuch as bimetal member 18 and the lower end of bracket 16 extends to theexterior of the housing. The outer end of bracket 16 is provided with anelectrical connector 16a for securing an electrical conductor thereto toform a connection to the breaker. The circuit through the breaker iscompleted from the lower end of bimetal member 18 through one or moreflexible electrical conductors 20 to a movable contact finger 22 andthrough the movable contact 22a secured thereto and a stationary contact23a to an external connector clip 23 for connecting the breaker to anexternal circuit. An overcenter tension spring 24 connects the lower endof contact finger 22 to the central portion of latch lever 14. Aresetting spring 25 is tensioned between the left leg of laatch lever 14and a projection in base 2.

A magnetic pole piece 26 is pivotally supported at its upper end onopposed projections in the base and cover. Pole piece 26 is provided atits mid-portion with a substantially longitudinal U-shaped portionsurrounding bimetal member 18 on three sides. The current flowing inbimetal member 18 energizes the magnetic pole piece and the elongatedends of the legs of the U-shaped portion form magnetic pole faces forattracting an elongated armature 28. Armature 28 is pivoted at its upperend in suitable alined cavities 30 in base 2 and cover 4. Armature 28extends downwardly from its pivot alongside magnetic pole piece 26 andis normally spaced there-from for attraction by the latter. A metallicstrip member 32 is rigidly secured adjacent the lower end of armature28. Member 32 is bent so that its free end diverges from armature 28into engagement with the lower yoke portion of latch latch 12 tomaintain engagement between the lower end of latch 12 and a suitablecatch 14a on latch lever 14. While metallic member 32 is preferably acompensating bimetallic member for altering the operation of the breakerto compensate for ambient temperature changes, it will be understoodthat it may instead comprise a single stiff but resilient piece ofmetallic material attached to armature 28 if compensation is notrequired.

The central portion of operating handle 8 diverges downwardly into asubstantiallysemi-circular or semicylindrical portion 8a to affordrestricted rotation of the handle in the housing. The axis of rotationof such semicylindrical portion is provided with a pair of journals 8bextending in opposite directions laterally of the operating handle forpivoting the latter in the base and cover. The lower portion of handle 8is bifurcated into a pair of like parallel enlarged portions 8claterally spaced in the direction of the aforementioned axis. Theseparallel enlarged portions are provided at the right-hand sides thereofwith alined holes 8d and at the lower central portion with alined holes8e for receiving the outwardly bent end portions of the legs of latch 12and contact finger 22, respectively, to pivotally support the latch andcontact finger on the operating handle. The yoke portion of latch 12 isflattened into a substantially rectangular cross-section and the uppersurface thereof is formed at a predetermined downward slope toward latchlever 14 and at a small downward angle from a plane normal to the planeof the latch. This downward angle is sufficient to afford an unstablesystem. Thus, the sloped portion of the latch engages catch 14a on thelatch lever when a predetermined bias force is applied thereto throughcompensating bimetal member 32 but slips oif therefrom to trip thebreaker when such force is reduced or removed. It will be apparent thatlatch 12 and contact finger 22 may be assembled on the operating handleby squeezing the free ends of the spaced legs thereof toward one another, inserting such ends between the spaced portions of the handle andallowing the outwardly bent portions of the latch and contact finger tospring into holes 8d and 8e, respectively. The central portion of thecavity in base 2 is provided with a projection 34 molded therein forguiding latch lever 14 and a Wall 36 extends upwardly into such cavityto form a stop for the right leg of latch lever 14 when the breaker istripped. Terminal bracket 16 is provided intermediate its ends with athreaded hole [or receiving an adjusting screw 38- threaded thereintoand extending through a slot in a wall of the base. Base 2 and cover 4are provided with a one-way slot 40 for receiving a rating card 42overlying and concealing the head of adjusting screw 38.

Magnetic pole piece 26 is provided at its pivotal end integrallytherewith with a pair of spaced circular portions 260 having alinedbearing apertures for receiving the opposed projections molded in thebase and cover. The other end of pole piece 26 is bent at a right anglethereto and is provided with a laterally extending projection 26b forengaging a molded projection 44 in base 2 to limit the clockwise piovtalmovement of the pole piece. Armature 28 has a T-shaped upper endportion, the extremities of the cross on the T being received incavities 30 in the base and cover for pivotally supporting the armature.

An important feature of the invention is the provision of a mechanismfor applying a biasing force to latch 12 to maintain engagement thereofwith catch 14a on latch lever 14. To this end, there is provided a pairof slide plates 46 and 48, more clearly shown in FIGS. 2 and 3. Theseslide plates are arranged in abutting relation and are slidably guidedin opposed grooves 50 and 52 in base 2 and cover 4. Slide plates 46 'and48 are provided with substantially I-shaped apertures 46a and 48aadjacent their right-hand ends which may be held slightly out ofregistration as shown by dotted lines in FIG. 2 by having portions ofthe plates hearing against bimetal member 18 and armature 28, theopposed projections extending into these apertures being received Withinthe opposite ends of a helical compression spring 54. Spring 54 andgrooves 50 and 52 maintain the slide plates in abutting relation and thespring biases apertures 46a and 48a toward registration. Plates 46 and48 are relatively slidably movable against the compressive force ofspring 54. Plate 46 is provided at its left-hand end with a stepped.slot 46b accommodating the free end of armature 28 against shoulders46c thereof. Plate 48 is provided at its left-hand end with a slot 48])extending inwardly a predetermined distance to clear the free end ofarmature 28 affording magnetic tripping with-out moving bimetal member18 and a rectangular aperture 480 accommodating the reduced free end ofbimetal member 18 which also extends freely through the narrow portion46d of the slot in plate 46 as shown in FIGS. 2 and 3.

It will be apparent that shoulders 46c and aperture 480 maintainarmature 28 separated from bimetal member 18 but that armature 28 iscapable of movement toward bimetal member 18 against the force of spring54. A resilient force is transmitted from the left end of spring 54through slide plate 46, armature 28 and member 32 to maintain latch 12in engagement with catch 14a on the latch lever, the right end of spring54 being held stationary by bimetal 18 acting through plate 48. Also,the slide plate assembly is free to move in the right-hand directionwhen bimetal meber 18 flexes after the bimetal has flexed enough tobring the plate apertures into registration since the compression springis in series with the latch maintaining reactive force imposed by thefixed bimetal 18.

Let it be assumed that a small overload current flows in thermal bimetalmember 18. As the latter heats, its lower end in FIG. 1 flexes or bendsin the right-hand direction. It will be apparent from FIG. 2 thatinitial movement of the lower end of the bimetal member in theright-handdirection allows spring 54 to move lower slide plate 48 in theright-hand direction. Such movement brings apertures 46a and 48a in theslide plates into closer registration with one another and reduces thecompression in spring 54. This action correspondingly reduces thefprceapplied through armature 28 and member 32 to latch 12 and reducesthe externally applied stress on bimetal member 18. When the aperturesin the slide plates register with one another and spring 54 has expandedas far as it can go wherein it is confined, the stress on bimetal member18 has been reduced and the left-hand directed force normally appliedthrough member 32 against latch 12 has been reduced. Further bending ofbimetal member 18 causes movement of the two slide plates and the springas a unit in the right-hand direction. With continuing movement, latch12 slips ofi catch 14,to trip latch lever 14 and open the contacts.

If a sudden large overload current flows in bimetal member 18, magneticpole piece 26 is energized sufficiently to attractarmature 28 thereto.This causes slideplate 46 to slide in the right-hand direction relativeto slide plate 48, the latter being restrained by bimetal member 18.Spring 54 is compressed. As a result, the bias force is reduced andlatch 12 slips off catch 14a to trip the breaker. When the overloadcurrent terminates, plate 46 is free to move in the left-hand directionto register apertures, 46a and 48a and restore the "armature back in theleft-hand direction thereby to relieve the stress on bimetal member 18.When the contacts are reclosed, latch 12 again bears against member 32so that plates 46 and48 againassurne .the position shown in FIG. 2 andare biased by force of spring 54.

It will be apparent that the invention afiords accurate control of thetripping point of the breaker. Spring 54 acting through slide plates 46and 48 resiliently maintains proper separation between bimetal member 18and armature 28 and there is no lost motion therebetween. The bias forceapplied to latch 12 originates as a stress in the bimetal member 18,decreases as the bimetal heats and deflects and becomes zero,eliminating stress in the bimetal, as soon as the breaker trips. As suchbias force is applied by use of the bimetal member as a reactivesupport, accurate adjustment thereof is afiorded at adjusting screw 38.

Since the circuit breaker described in connection with FIGS. 1-3 is ofthe unstable latch type, it is only necessary to reduce or remove theforce applied to latch 12 to cause the breaker to trip. When such forceis sufficiently reduced or removed, the angular surface of the loweryoke portion of latch 12 will slip oit catch 14a,of the latch lever toallow the breaker to trip and open the contacts. Overcenter spring 24rotates latch lever 14 clockwise until the lower end of the right-handleg of the latch lever stops against wall 36. In this position, thelatch lever has carried the upper end of overcenter Spring 24 pastcontact finger 22. As a result, the tension in spring 24 snaps thecontacts open and pulls the contact finger upwardly causing rotation ofoperating handle 8 clockwise fromits on position to its off position.Thereafter, resetting spring 25 restores latch lever 14 partiallycounterclockwise since the tension in spring 24 has been relieved sothat catch 14a moves above the yoke portion of latch 12. In this resetposition, the breaker contacts can be reclosed by merely turning theoperating handle back to its on position.

From the foregoing, it will be apparent that aperture 46a in upper slideplate 46 may be smaller than, equal to or larger in the horizontaldirection in FIG. 2, than the corresponding aperture 48a in lower slideplate 48. Under any one of these three conditions, there will be no lostmotion between movement of thermal member 18 and tripping of the latch.Apertures 46a or 48a in either slide plate can be made larger or smallerat either end without altering the operation of the system of partsbecause both plates are still free in any instance to move as a unit topermit tripping and the spring will be contained in one plate or theother to relieve the bimetal of external stress. One example of amodified slide plate 56 that could be used in place of slide plate 46 isshown in FIG. 4. It will be seen that slide plate 56 is similar to slideplate 46 except that the right-hand end has been cut off leavingaperture 56a open. This represents an aperture that is larger only atits right-hand side than the aperture in lower slide plate 48. Withmovement of the bimetal, spring 54 would be restricted by aperture 48afrom further expansion. Then, the slide plates and spring can begin tomove as a unit with further movement of the thermal member after theleft-hand edges of the apertures come into registration. After tripping,spring 54 would be confined in aperture 48a, relieving bimetal 18 ofexternal mechanical stress.

Referring to FIGS. 5, 6 and 7, there is shown a modified circuit breakerof the stable'latch type. In this modification, reference characterslike those in FIGS. 1-3 have been used for like parts. This modificationdiffers from the unstable latch type breaker hereinbefore described inthe structures of the latch 58, the armature 60 and the upper slideplate 62. The lower yoke portion of latch 58 is provided with anuninclined or straight surface 5811 so that. a force need not be appliedto hold the latch engaged with catch 14a on latch lever 14. Instead, thelatch remains in engagement with the catch and must be pulled therefromto trip the circuit breaker. For this purpose, armature 60 .is providedwith a hook 60a in the form of a spring wire, more fully described in M.F. Koenig et al. copending application Serial No. 261,345, filedFebruary 27, 1963, now patent No. 3,214,535, dated October 26, 1965, andassigned to the assignee of this invention. This wire is secured at itsupper end to the upper end portion of the armature as by welding andextends downwardly therefrom so that its lower. end enters behind theyoke portion of latch 58 on one side of latch lever 14. It will be seenthat if thelower end of the armature is moved in the right-handdirection, hook 60a pulls the latch from the catch to trip the breaker.Otherwise, armature 60 is like armature 28 and is provided with acompensating bimetal member 60!: similar to member 32 in FIG. 1.

To enable movement of the armature in response to thermal action, amodified upper slide plate 62 is provided. This slide plate is similarto slide plate 46 in that it is provided with an aperture 62a for thecompression spring and a stepped slot at the left-hand end having a wideportion 62b, a pair of shoulders 62c and a narrower deep portion 62d.This slide plate differs from slide plate 46 in that wide portion 62b ofthe slot is provided with a pair of inwardly projecting ears 62creducing the width of this portion of the slot to correspond to thewidth of narrow portion 62d. Ears 622 are spaced in the left-handdirection from shoulders 620 to just receive the opposite edge portionsof armature 60 freely there-between. As shown in FIG. 7, shoulders 62cand ears 62e are chamfered on the upper side to allow free pivoting ofthe armature a small amount relative to the slide plate and theshoulders and ears confine the armature to avoid significant l-ostmotion when the slide plate is moved in the righthand direction from theposition shown in FIGS. 5 and 6.

As shown in FIG. 6, when the circuit breaker is closed, thermal bimetalmember 18 holds plate 48 from moving in the right-hand direction due tothe fact that the end of the bimetal extends through hole 480 in theslide plate. Compression spring 54 biases slide plate 62 in the lefthanddirection because apertures 48a and 62a are offset from one another. Asa result, shoulders 62c push on armature 60 and hold the'upper end ofcompensating bimetal 60b snugly against the lower end of latch 58. Underthis condition, hook 60a is stressed so that it bears against the leftside of latch 58. When the operating handle is turned oif and latch 58lowers, hook 60a springs into engagement with the upper end of bimetal60b. When the latch is raised, it separates hook 60a from thecompensating bimetal member.

When thermal bimetal member 18 heats and bends in the right-handdirection, spring 54 moves slide plate 48 in the right-hand direction tothe extent permitted by the thermal member and the stress on the latterdecreases. When the apertures in the slide plates register with oneanother to restrict further expansion of spring 54, the stress on thethermal member 18 becomes relieved and bimetal member 18 will begin tomove the slide plates and spring 54 as a unit in the right-handdirection. Ears 62e will pull on the armature to move the armature withthe thermal member 18. As a result, hook 60 will pull latch 58 loosefrom catch 14a to trip the breaker.

Aperture 62a in the upper slide plate must be equal in its horizontaldimension in FIGS. and 6 to aperture 48a in the lower slide plate andmay not be smaller or larger if lost motion is to be avoided. Ifaperture 62a is smaller at its right-hand side, there will be lostmotion from the point where the right-hand edges pass throughregistration and the spring stops expanding to the point where theirleft-hand edges register and slide plate 48 starts to push the spring.If aperture 62a is made smaller at its left-hand side, there will belost motion from the point where the right-hand edges of the aperturespass through registration to the point where their left-hand edgescoincide unless bimetal 18 sooner bears on the bottom of slot 62d. Whenthe apertures are the same size, as shown, they will first register asthe bimetal bends, then the bimetal will push slide plate 48 which willpush the spring and the spring will push slide plate 62 to pull thearmature to the right to trip the breaker without lost motion. Ifaperture 62a is made larger at its left-hand side, there will be lostmotion from the point where the left-hand edges of the apertures passthrough registration until the right-hand edges thereof register. Ifaperture 62:: is made larger at its right-hand side, there will be lostmotion from the point where the lefthand edges of the apertures passthrough registration until their right-hand edges register unlessbimetal 18 sooner bears on the bottom of slot 62d. If the righthand endportion of slide plate 62 is cut off to enlarge the aperture in themanner of FIG. 4, the breaker will not trip until bimetal 18 engages thebottom of slot 62d and pushes slide plate 62 to the right.

To summarize, if aperture 62a is made smaller or larger than aperture48a, as it should not be, slide plate 62 will remain stationary as slideplate 48 continues to move with the thermal member after spring 54 isrestricted from further expansion by the smaller aperture as the casemay be. This might make the tripping point uncertain because the lostmotion introduced permits uncontrollable movement of the parts.Consequently, in this modification, aperture 62a is made equal toaperture 48a.

Under magnetic trip, pole piece 26 attracts armature 60 thereto. Thearmature moves slide plate 62 against the force of spring 54 while slideplate 48 may remain stationary depending upon bimetal activity and hook60a pulls the latch from the catch to trip the breaker.

While the apparatus hereinbefore described is effectively adapted tofulfill the objects stated, it is to be understood that I do not intendto confine my invention to the particular preferred embodiments ofcircuit breake mechanisms disclosed, inasmuch as they are susceptible ofvarious modifications without departing from the scope of the appendedclaims.

I claim:

1. In a circuit breaker of the type having a spring biased mechanism foroperating the breaker between circuit-closed and circuit-open conditionsand an operatlng lever for actuating said operating mechanism, thecombination comprising:

latch means acting on said operating mechanism to maintain the latter inits circuit-closed condition and being releasable in response to anabnormal electrical condition to trip said operating mechanism to itscircuit-open condition;

a thermal responsive device having a portion which moves when heatedunder the influence of an excessive electro-thermal condition in thebreaker;

and means coupling said movable portion to said latch means foreffecting the release of the latter upon predetermined movement andbeing normally effective to apply a bias tending to separate saidmovable portion of said thermal responsive device from said latch meansto prevent lost motion therebetween when said movable portion starts tomove and comprising:

means in said coupling means responsive to movement of said movableportion for decreasing said bias thereby to reduce upon tripping thestress imposed on said thermal responsive device when it is hot.

2. The invention defined in claim 1, wherein said bias decreasing meanscomprises:

means for reducing the stress being imposed on said thermal responsivedevice to zero value.

3. The invention defined in claim 1, wherein said bias decreasing meanscomprises:

means for reducing the stress being imposed on said thermal responsivedevice to zero value before release of said latch means.

4. The invention defined in claim 1, wherein:

said latch means is unstable and maintains said operating mechanism incircuit-closed condition in response to the bias of said coupling meansand releases to trip said operating mechanism in response to said biasdecreasing means.

5. The invention defined in claim 1 wherein:

said latch means is stable and maintains said operating mechanism incircuit-closed condition until a force is applied to release it;

said bias decreasing means comprising means for reducing the stressbeing imposed on said thermal responsive device to zero value under theinfluence of said movable portion;

and said coupling means comprising means responsive to continuedmovement of said movable portion after said stress has been reduced tozero value for pulling said latch means apart to trip said operatingmechanism and said thermal responsive device again becoming unstressedfollowing said tripping.

6. In a circuit breaker of the type having an overcenter spring biasedmechanism for operating the breaker between contacts-open andcontacts-closed positions and a manual operating lever for actuatingsaid operating mechanism, the combination comprising:

latch means acting on said operating mechanism to maintain the latter inits contacts-closed position and being releasable in response to asustained overload current condition or an extreme overload currentcondition to trip said operating mechanism to its contacts-openposition;

a thermal current responsive bimetal member anchored at one portion sothat another portion deflects when 9. heated by sustained overloadcurrent flow therethrough;

a magnetic pole piece mounted adjacent said bimetal member forexcitation by the latter in response to an extreme overload current flowcondition;

an armature pivoted. at one end and extending substantially parallel tothe bimetal member to form a magnetic air gap with the pole piece;

means connected to said armature for releasing said latch means;

and means including confined resilient means normally coupling thedeflecting portion of said bimetal member to said armature to transmit aforce before and during predetermined deflection of said bimetal memberthrough said armature to the latch means while imposing a correspondingreactive stress in said bimetal member and to permit the armature tomove without the bimetal member moving.

7. Theinvention defined in claim 6, wherein said confined resilientmeans comprises:

means for eliminating the stress applied to said bimetal member when thedeflecting portion thereof has moved tripping the breaker.

8. The invention defined in claim 6, wherein said confined resilientmeans comprises:

means for eliminating the stress applied to said bimetal member when thearmature has moved tripping the breaker and the armature has restored.

9. The invention defined in claim 6, wherein said resilient meanscomprises:

a pair of slide plates lying flat against one another;

means mounting said plates for sliding movement together and relative toone another;

a spring biasing one of said plates in one direction against saidarmature and biasing the other plate in the other direction against thedeflecting portion of said bimetal member to transmit a force to saidlatch means, said other plate sliding relative to the first plate whensaid bimetal member deflects;

and means comprising said spring for restricting the sliding movement ofsaid other plate relative to said first plate and for eliminating thestress in said bimetal member when the breaker trips.

10. The invention defined in claim 9, wherein sufficient clearance isprovided between the armature and said other plate to allow movement ofthe armature in response to magnetic force to slide said first plate andcompress said spring and thereby to release said latch means withoutmoving said other plate or said bimetal member.

11. The invention defined in claim 9, wherein said means comprising saidspring consists of:

a pair of ofiset but overlapping apertures in said slide plates;

said spring being in compression within said apertures to bias saidplates in opposite directions thereby to stress said bimetal member;

and relative movement of said plates by said spring when said bimetalmember deflects causing elimination of said stress when at least firstsides of said apertures move into registration preventing furtherexpansion of said spring.

12. The invention defined in claim 11, wherein said other plate isprovided with a second aperture accommodating the deflecting end of saidbimetal member.

13. The invention defined in claim 12, wherein said first plate isprovided with a slot through which said himetal member extends withsuflicient clearance to permit the latter to deflect free of said firstplate.

14. The invention defined in claim 11, wherein said first plate isprovided with means confining the free end of said armature for movingsaid armature to release said latch means in response to furtherdeflection of said bimetal member after said spring has expanded as faras it can go.

15. The invention defined in claim 11, wherein the spring receivingaperture in said first plate is as large in the direction of springexpansion as the corresponding aperture in the other plate.

16. The invention defined in claim 11, wherein the spring receivingaperture. in said first plate is smaller in the direction of springexpansion than the corresponding aperture in the other plate.

17. The invention defined in claim 11, wherein the spring receivingaperture in said first plate is larger in the direction of springexpansion than the corresponding aperture in the other plate.

18. In an electro-thermal and electromagnetic trip circuit breaker, thecombination comprising:

a spring actuated mechanism for tripping the breaker from contact-closedto contact-open position and an operating lever for setting the trippingmechanism in contact-closed position;

latch means for maintaining said tripping mechanism in contact-closedposition;

an elector-thermal member connected in the electric circuit of thebreaker for flexing in response to continuous small overload currentflow therethrough;

a magnetic member adjacent said electro-thermal member;

a pivoted armature assembly arranged for magnetic attraction by saidmagnetic member in response to large overload current flow through saidelectrothermal member and engaging said latch means;

and means coupling said armature assembly and said electro-thermalmember and comprising:

means subjecting said electro-thermal member to an externally appliedstress prior to and as it deflects under continuous small overloadcurrent and being bodily movable with said deflecting electro-thermalmember effecting movement of said armature assembly to release saidlatch means and cause tripping of the breaker;

resilient means allowing movement of said armature assembly under largeoverload current without moving said electro-thermal member to causetripping of the breaker;

and means removing all externally applied stress from saidelectro-thermal member upon either thermal or magnetic tripping of thebreaker to prevent imposing a set therein when it is hot.

19. The invention defined in claim 18, wherein said coupling means alsocomprises:

means including said resilient means for returning said armatureassembly into engagement with said latch means when said electro-thermalmember cools and restores following thermal tripping thereby to insurelatching of said latch means onto said tripping mechanism when saidoperating lever is reset.

20. Ina circuit breaker of the type having a spring biased mechanism foroperating a breaker between cir-' cuit-closed and circuit-open conditionand an operating lever for actuating said mechanism, the combinationcomprising:

latch means acting on said operating mechanism to maintain the latter inits circuit closed condition and being releasable to trip said operatingmechanism to its circuit open condition;

a thermal responsive device having a portion which moves when heatedunder the influence of an excessive electro-thermal condition in thebreaker;

a magnetically responsive device having a movable portion responsive toexcessive electromagnet conditions in the breaker;

and means coupling each said movable portion to said latch means foreffecting the release of the latter upon predetermined movement andbeing capable of permitting action of the magnetically responsivedevicewithout motion of the thermal responsive device which coupling meanseliminates external mechani- References Cited by the Examiner UNITEDSTATES PATENTS 3/1963 Koenig et a1. 200-88 4/1963 Gelzheiser 200-88 12References Cited by the Applicant UNITED STATES PATENTS 3,110,78611/1963 Gelzheiser.

BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, JR., Assistant Examiner.

1. IN A CIRCUIT BREAKER OF THE TYPE HAVING A SPRING BIASED MECHANISM FOROPERATING THE BREAKER BETWEEN CIRCUIT-CLOSED AND CIRUCIT-OPEN CONDITIONSAND AN OPERATING LEVER FOR ACTUATING SAID OPERATING MECHANISM, THECOMBINATION COMPRISING: LATCH MEANS ACTING ON SAID OPERATING MECHANISMTO MAINTAIN THE LATTER IN ITS CIRCUIT-CLOSED CONDITION AND BEINGRELEASABLE IN RESPONSE TO AN ABNORMAL ELECTRICAL CONDITION TO TRIP SAIDOPERATING MECHANISM TO ITS CIRCUIT-OPEN CONDITION; A THERMAL RESPONSIVEDEVICE HAVING A PORTION WHICH MOVES WHEN HEATED UNDER THE INFLUENCE OFAN EXCESSIVE ELECTRO-THERMAL CONDITION IN THE BREAKER; AND MEANSCOUPLING SAID MOVABLE PORTION TO SAID LATCH MEANS FOR EFFECTING THERELEASE OF THE LATTER UPON PREDETERMINED MOVEMENT AND BEING NORMALLYEFFECTIVE TO APPLY A BIAS TENDING TO SEPARATE SAID MOVABLE PORTION OFSAID THERMAL RESPONSIVE DEVICE FROM SAID LATCH MEANS TO PREVENT LOSTMOTION THEREBETWEEN WHEN SAID MOVABLE PORTION STARTS TO MOVE ANDCOMPRISING: MEANS IN SAID COUPLING MEANS RESPONSIVE TO MOVEMENT OF SAIDMOVABLE PORTION FOR DECREASING SAID BIAS THEREBY TO REDUCE UPON TRIGGINGTHE STRESS IMPOSED ON SAID THERMAL RESPONSIVE DEVICE WHEN IT IS HOT.